1. Technical Field
The present invention relates to a power amplifier pulse-modulating a drive waveform signal serving as a reference of a drive signal for driving an actuator, amplifying the power of the modulated signal, and outputting the amplified modulated signal as a drive signal.
2. Related Art
In comparison with an analog power amplifier linearly driving a pair of transistors connected in a push-pull manner, a digital power amplifier amplifying the power by switching, that is, digitally operating, switching elements connected in a push-pull manner has excellent efficiency and has been widely used.
When a drive signal is output to an actuator for ejecting a liquid from nozzles of a liquid jet printing apparatus using the digital power amplifier, a drive waveform signal serving as a reference of the drive signal is pulse-modulated into a modulated signal by the use of a modulation unit, the power of the modulated signal is amplified by the use of the digital power amplifier, an amplified digital signal is smoothed by the use of a low pass filter, and the resultant digital signal is output as the drive signal. The low pass filter reduces the frequency component of pulse modulation.
At this time, when the number of driven actuators varies, the frequency characteristic of a filter including the low pass filter and electrostatic capacitors of the actuators also varies, whereby the desired waveform precision of the drive signal cannot be obtained.
Therefore, as described in PCT publication No. WO2007/083669, the applicant of the invention provided a front stage of the modulation unit with an inverse filter capable of providing the desired waveform precision of the drive signal regardless of the number of driven actuators.
However, since the low pass filter actually used in the digital power amplifier is a high-order filter of a third order or higher, a low-order inverse filter of a first or second order may not provide the desired waveform precision of the drive signal.
On the contrary, when a high-order filter of a third order or higher is used as the inverse filter, there is a problem that the configuration becomes complicated.